Process for producing hexabromocyclododecane

Abstract

This invention relates to the production of an hexabromocyclododecane product, which process comprises brominating cyclododecatriene in the presence of a 1,4-dioxane and water based solvent and from about 0.5 to about 30 wt % bromide ion in the liquid phase of the reaction mass. Optional post-reaction heat treatment in a finishing step increases process yields if needed. The hexabromocyclododecane product is unrecrystallized and contains no more than about 1.5 wt % tetrabromocyclododecene impurities.

Description

This invention concerns an improved process for the production of hexabromocyclododecane. The process produces a low-melting, highly pure hexabromocyclododecane product.Hexabromocyclododecane (1,2,5,6,9,10-hexabromocyclododecane) is a well established flame retardant for use in various thermoplastics. This compound is usually produced as a mix of its three stereoisomers, the alpha, beta and gamma isomers. It is preferred that the gamma isomer comprise about 70 wt % of the mix. Hexabromocyclododecane is commercially available as a product which contains principally hexabromocyclododecane and lesser amount of impurities. A principal impurity is the underbrominated species, tetrabromocyclododecene. The tetrabromocyclododecene impurities can comprise up to 10 wt % of the hexabromocyclododecane product. Lesser impurities include the side-reaction products formed by the reaction of the brominating agent with cyclododecatriene, brominated cyclododecane and reactive solvents, e.g., alcohols...

AI Technical Summary

Benefits of technology

It has been discovered that by using a 1,4-dioxane-water solvent there is obtained, at reaction end, a reduction in the amount, i.e., to less than about 1.5 wt %, of tetrabromocyclododecene in the recovered hexabromocyclododecane product. (Unless otherwise stated, the wt % of the tetrabromocyclododecane, the isomers of hexabromocylododecane, by-product impurities, etc., which are recited herein are all based on the total weight of the recovered hexabromocyclododecane product of which they are a constituent.) Also achieved is good utilization of the brominating agent, e.g., bromine. Both of these benefits are the result of the aqueous 1,4-dioxane being relatively inert in the reaction while having good solubility for tetrabromocyclododecenes at the reaction temperature, e.g., 20 to 50.degree. C. By keeping most of the tetrabromocyclododecenes in solution during the reaction, it is more likely, over time and in some cases under heat, that the underbrominated species will be brominated to hexabromocyclododecane. Further, since aqueous 1,4-dioxane is relatively unreactive with the brominating agent, there are less by-product impurities formed and thus more brominating agent present in the reaction to promote the hexabromination of the tetrabromocyclododecenes. In addition, hexabromocyclododecane is relatively insoluble in the aqueous 1,4-dioxane solvents of this invention, thus very little is lost to the residual mother liquor after recovery of the precipitate. This, along with the perbromination of the tetrabromocyclododecene, promotes high yields.

While the aqueous 1,4-dioxane solvent system attenuates the formation of impurities and promotes the perbromination of tetrabromocyclododecene, this system does not produce a high gamma content. Generally, the gamma content will be about 50 wt %, the wt % being based on the total weight of brominated cyclododecatriene in the reaction mass. It has been discovered, however, that if the liquid portion of the reaction mass contains from about 0.5 to 30 wt %, and preferably from about 3 to about 30 wt %, bromide ion (Br.sup.-), then the gamma content will be enhanced to 65 to 75 wt % on the same basis. Most preferred amounts of bromide ion are in the range of from about 4 to about 13 wt %. The wt % values for the bromide ion are based on the total weight of the liquid portion of the reaction mass. It is theorized, though this invention is not to be limited to any one theory, that the bromide ion complexes with the brominating agent, e.g., bromine, and that the resulting complex selectively assists bromination of the sterically hindered intermediates which leads to the gamma isomer. Thus, the formation of the gamma isomer is facilitated.

It may be desirable, depending upon the economics of any particular process of this invention, for the practitioner to convert at least a part of the underbrominated cyclododecatriene to hexabromocyclododecane. Simple heating of the reaction mass will convert a significant amount of the tetrabromocyclododecene solutes in the reaction mass to hexabromocyclododecane which will almost all go towards the formation of the hexabromocyclododecane product precipitate. The heating step is without significant down-side in the processes of this invention as the inert 1,4-dioxane and water solvent does not react with reaction mass constituents which is unlike the situation which occurs when the solvent contains a reactive species, such as an alcohol. Thus, an advantage for the solvents of this invention is that a highly pure product containing no or little solvent derived by-products and little or no tetrabromocyclododecenes can be obtained directly without the need for further purification steps, e.g., recrystallization, which is indicated for systems using a reactive solvent such as alcohol.

Hexabromocyclododecane product yields can be increased by recycling the mother liquor, the wash liquor and their respective unfiltered solids to subsequent reactions.

Problems solved by technology

While the aqueous 1,4-dioxane solvent system attenuates the formation of impurities and promotes the perbromination of tetrabromocyclododecene, this system does not produce a high gamma content.